The present invention relates to the field of microwave ovens. More specifically, the present invention relates to improvements in microwave ovens having rotatable elements which "stir" the microwave energy for more nearly uniform cooking of each food body placed in the ovens.
It has long been recognized that microwave ovens offer advantageously rapid cooking of food bodies placed therein as compared with other types of ovens which heat food bodies from the outer surface of the food and rely on thermal conduction to heat the center. Because the microwave oven radiates microwave energy from a feed system into the oven cavity and the microwaves are absorbed by the food throughout its volume, the food is more rapidly brought to a temperature everywhere in its volume which suffices to cook the food. At the same time, however, the rapidity of cooking offered by microwave technique carries with it the unsatisfactory potential for undercooking some portions of the food when the rest is cooked until properly done, and for fully cooking such portions only if the rest is overdone. Such cold and hot spots can reduce the attractiveness of microwave oven technology if they cannot be eliminated by improvements in the technology.
The need for improvements has been recognized for many years in the prior art, which has provided various microwave "stirrers" for stirring up the heating pattern of the microwave energy and hopefully increasing the uniformity of cooking of food and other objects to be heated. This "stirring" is actually a combination of time-varying scattering, cavity perturbation, and alteration of cavity excitation.
Microwave ovens are usually metallic cavities provided with reclosable doors, and a magnetron or other generator of microwave power is coupled by means of a waveguide arrangement to the cavity. Some ovens are provided with turntables to turn the food in the cavity to increase uniformity of cooking. Other microwave ovens are provided with stirrers which look like propeller blades turning on a wall of the oven cavity at a distance from the opening of the waveguide into the cavity. Some other stirrers are provided so as to turn inside the waveguide itself, and not in the cavity. Still other stirrers are provided in the cavity over the opening of the waveguide into the cavity.
Truly effective stirring, or truly uniform cooking of all types and sizes of food objects, in a microwave oven is an objective perhaps more often hoped for than fully met in much of the prior art, and even if met, the stirring arrangement may entail substantial manufacturing cost. The complex geometry of microwave ovens and stirrers has defied effective mathematical analysis and prediction if only because the shape and position of food being cooked is changed from use to use. Accordingly, persons skilled in the art have been forced to use trial and error experimental techniques because the ability to predict superior performance in ovens with stirrers is so limited.
Thus, it is of considerable interest to the microwave oven art to learn new ways of obtaining more truly uniform cooking and heating without increasing cost of manufacture. It is of corresponding interest to the art to find new ways of obtaining at least comparable uniformity of cooking in microwave ovens while decreasing the cost of manufacture, so that the potential utility of microwave ovens to the general population and to specialized users can be more fully realized.